Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
A typical image reading apparatus typically generates an analog-image signal by causing light to perform sub-scanning with respect to a document and reading the document by a line sensor with a plurality of light receiving elements arranged in a main-scanning direction. Some line sensors include charge coupled devices (CCDs) in parallel (the main-scanning direction in this example) with respect to the plurality of light receiving elements, and those sensors are referred to as “CCD line sensor” in this description. The CCD line sensor accumulates electric charges that are photoelectrically converted by the plurality of light receiving elements in each potential well (a well of an electric charge) formed by a CCD element according to each pixel. The electric charges accumulated in each potential well are transferred all at once in a sub-scanning direction with respect to a shift register arranged in the main-scanning direction (what is called a bucket brigade).
A light amount of a light source in image reading by a CCD line sensor has been set as a result of the following trade-off. (1) A large amount of electric charges accumulated in each potential well enables increasing an SN ratio. (2) A large amount of electric charges causes a phenomenon (smear) where electric charges leak in a direction perpendicular to a transfer direction in transferring of the electric charges. Considering such trade-off, there is proposed a technique that determines a temporal variation pattern of a light amount from a light source and then adjusts a light-amount level value of the light source based on the determined variation pattern. This technique discloses that it is possible to obtain an image with a favorable SN ratio at high speed by setting a light-amount level to an optimum value in light-amount adjustment such as power activation.